Optical fiber and method for manufacturing optical fiber

Abstract

An optical fiber (10) provided with: a small-diameter part (13); a large-diameter part (14) having a larger diameter than the small-diameter part (13); and a tapered part (15) positioned between the small-diameter part (13) and the large-diameter part (14) and having a diameter that gradually decreases from the large-diameter part (14) side toward the small-diameter part (13) side, an arithmetic mean roughness Ra, which is the surface roughness of the tapered part (15), being less than 0.15 μm.

Description

Optical Fiber and Method for Manufacturing the Same

[0001] The present invention relates to an optical fiber and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2024-224849 filed in Japan on December 20, 2024, and incorporates its content herein by reference.

[0002] Conventionally, an optical connector having a structure in which a plurality of optical fibers (single-core fibers) are inserted into fiber holes of a ferrule is known. According to such an optical connector, a plurality of optical fibers can be connected to a connection target such as a multi-core fiber. At this time, in order to align the cores of the plurality of optical fibers with the arrangement of the cores of the multi-core fiber, the tip of the optical fiber may be thinned. In Patent Document 1, a thin diameter portion and a taper portion are formed on the optical fiber by etching the optical fiber.

[0003] Japanese Patent Application Laid-Open No. 2012-220504

[0004] Since the diameter of the taper portion of the optical fiber changes along the longitudinal direction, it is a portion that is likely to break due to the curing shrinkage of the adhesive for fixing the optical fiber to the ferrule, or due to stresses such as the heat test and vibration test of the optical fiber. In particular, if the smoothness of the surface of the taper portion is insufficient, excessive stress is generated in the taper portion and it is likely to break, and sufficient tensile strength of the optical fiber may not be obtained.

[0005] The present invention has been made in consideration of such circumstances, and an object thereof is to provide an optical fiber and a method for manufacturing the same that can obtain sufficient tensile strength.

[0006] The optical fiber according to Aspect 1 of the present invention includes a thin diameter portion, a thick diameter portion having a larger diameter than the thin diameter portion, and a taper portion located between the thin diameter portion and the thick diameter portion, the diameter of which gradually decreases from the thick diameter portion side toward the thin diameter portion side, and the surface roughness of the taper portion, the arithmetic mean roughness Ra is less than 0.15 μm.

[0007] Aspect 2 of the present invention is the optical fiber according to Aspect 1, wherein the arithmetic mean roughness Ra of the taper portion is less than 0.01 μm.

[0008] A third aspect of the present invention is an optical fiber according to the first aspect, wherein the surface roughness of the tapered portion is such that the maximum height roughness Rz is less than 0.50 μm.

[0009] Aspect 4 of the present invention is an optical fiber according to aspect 1, wherein the surface roughness of the tapered portion is such that the arithmetic mean height Sa is less than 0.15 μm.

[0010] Aspect 5 of the present invention is an optical fiber according to aspect 1, wherein the surface roughness of the tapered portion is such that the maximum height Sz is less than 1.50 μm.

[0011] Embodiment 6 of the present invention is an optical fiber according to any one of embodiments 1 to 5, wherein the length of the tapered portion in the longitudinal direction of the optical fiber is 0.5 to 15 mm.

[0012] Embodiment 7 of the present invention is an optical fiber according to any one of embodiments 1 to 6, wherein the taper angle θ is defined as the angle between the tangent to the surface of the tapered portion and the axis of the optical fiber along the longitudinal direction of the optical fiber, and such that 0.1 degrees < θ < 5 degrees.

[0013] A method for manufacturing an optical fiber according to aspect 8 of the present invention comprises an etching step of etching the optical fiber by immersing it in an etching solution and moving it up and down, wherein in the etching step, the optical fiber is moved up and down continuously multiple times such that the stopping time of the up and down movement of the optical fiber is 1 second or less.

[0014] Aspect 9 of the present invention is a method for manufacturing optical fibers according to aspect 8, wherein in the etching step, a plurality of optical fibers are moved up and down simultaneously, and the distance between the plurality of optical fibers is 1 mm or more.

[0015] According to the above aspects of the present invention, it is possible to provide an optical fiber capable of obtaining sufficient tensile strength and a method for manufacturing an optical fiber.

[0016] This is a perspective view of an optical connector equipped with an optical fiber according to the first embodiment. This is a cross-sectional view taken along the line II-II in Figure 1. This is a side view of the optical fiber according to the first embodiment. This is a schematic diagram of a manufacturing apparatus used in the manufacturing method of the optical fiber according to the first embodiment. This is a diagram illustrating the manufacturing method of the optical fiber according to the first embodiment. This is a schematic diagram of a manufacturing apparatus used in the manufacturing method of the optical fiber according to the second embodiment. This is a graph showing the relationship between the surface roughness (arithmetic mean roughness) of the optical fiber and the tensile strength of the optical fiber.

[0017] (First Embodiment) The optical fiber and method for manufacturing the optical fiber according to the first embodiment will be described below with reference to the drawings. As shown in Figure 1, the optical connector 1 comprises a plurality of optical fibers 10, a ferrule 20, two positioning pins 40, and a boot 50. The optical connector 1 does not necessarily have to include the positioning pins 40 and the boot 50.

[0018] The ferrule 20 has a connecting end face 20a, a rear end face 20b, a fiber hole 21, an injection hole 22, two positioning holes 23, and an introduction hole 24 (see Figure 2). The connecting end face 20a is the surface that abuts against other connectors when the optical connector 1 is connected to other connectors. The fiber hole 21 and the two positioning holes 23 open to the connecting end face 20a.

[0019] Multiple optical fibers 10 are introduced into a single fiber hole 21. As shown in Figure 1, positioning pins 40 are inserted through each of the two positioning holes 23. The illustrated optical connector 1 is male and has positioning pins 40. However, the optical connector 1 may be female and not have positioning pins 40.

[0020] (Direction Definitions) In this specification, the direction in which the optical fiber 10 extends is referred to as the Z direction, axial Z, or longitudinal direction Z. The longitudinal direction Z coincides with the direction in which the fiber hole 21 extends. Along the longitudinal direction Z, the direction from the rear end face 20b of the ferrule 20 toward the connecting end face 20a is referred to as the +Z direction, forward, or tip side. The direction opposite to the +Z direction is referred to as the -Z direction, rear, or base side. In this embodiment, one direction perpendicular to the longitudinal direction Z is referred to as the first direction X. The first direction X is also the direction in which the two positioning holes 23 are aligned. The direction perpendicular to both the longitudinal direction Z and the first direction X is referred to as the second direction Y.

[0021] At the connection end face 20a, the fiber hole 21 is positioned between two positioning holes 23. The injection hole 22 opens into one end face of the ferrule 20 facing the second direction Y. The injection hole 22 communicates with the internal space of the ferrule 20 and the fiber hole 21. When the optical connector 1 is assembled, adhesive 30 is injected into the interior of the optical connector 1 through the injection hole 22. The injected adhesive 30 also enters the interior of the fiber hole 21. The introduction hole 24 is located behind the fiber hole 21. The introduction hole 24 communicates with the fiber hole 21. The introduction hole 24 opens into the rear end face 20b. Multiple optical fibers 10 are inserted into the fiber hole 21 through the introduction hole 24.

[0022] As shown in Figure 3, the optical fiber 10 has a glass portion 11 and a cladding C. The glass portion 11 is made of, for example, quartz glass. The glass portion 11 has a core and cladding (not shown).

[0023] The coating C partially covers the glass portion 11 and serves to protect the glass portion 11. The coating C is formed of a resin or the like. For example, the material of the coating C may be a UV-curing resin. At the front end of the optical fiber 10, the coating C is not provided, and the glass portion 11 is exposed. In other words, the glass portion 11 has a bare portion 12 extending from the coating C. The bare portion 12 is inserted through the fiber hole 21 of the ferrule 20.

[0024] The bare portion 12 has a narrow diameter portion 13, a wide diameter portion 14, and a tapered portion 15. The wide diameter portion 14 has the same diameter as the portion of the glass portion 11 covered by the coating C. The narrow diameter portion 13 is located on the tip side of the bare portion 12. The narrow diameter portion 13 has a smaller diameter than the wide diameter portion 14. The narrow diameter portions 13 of multiple optical fibers 10 are inserted into one fiber hole 21 of the ferrule 20.

[0025] The tapered portion 15 is located between the narrow diameter portion 13 and the wide diameter portion 14. The diameter of the tapered portion 15 gradually decreases from the wide diameter portion 14 side towards the narrow diameter portion 13 side. The length of the tapered portion 15 in the longitudinal direction Z is in the range of 0.5 mm to 15 mm. The tapered portion 15 has a first end 15a (base end) connected to the wide diameter portion 14 and a second end 15b (tip end) connected to the narrow diameter portion 13. The diameter of the second end 15b is the same as the diameter of the narrow diameter portion 13, and the diameter of the first end 15a is the same as the diameter of the wide diameter portion 14. The diameter of the tapered portion 15 continuously decreases from the first end 15a to the second end 15b. The tapered portion 15 does not have a portion where the diameter is constant in the longitudinal direction Z. The tapered portion 15 has no inflection points in the approximation line of the change in diameter.

[0026] The surface of the tapered portion 15 is formed smoothly. Specifically, the surface roughness (arithmetic mean roughness) Ra of the tapered portion 15 is less than 0.15 μm. It is more preferable that the surface roughness Ra of the tapered portion 15 is less than 0.01 μm. When the angle between the tangent to the surface of the tapered portion 15 and the axis O along the longitudinal direction Z of the optical fiber 10 is defined as the taper angle θ, the taper angle θ is 0.1 degrees < θ < 5 degrees. In the tapered portion 15, the taper angle θ may be constant in the longitudinal direction Z, or it may vary in the longitudinal direction Z. The outer shape of the tapered portion 15 has symmetry about the axis O. More specifically, the cross section of the tapered portion 15 perpendicular to the longitudinal direction Z is circular over the entire longitudinal direction Z, with the axis O as the center.

[0027] The narrow-diameter portion 13 and the tapered portion 15 can be formed by immersing the end of the glass portion 11, which has a constant diameter in the longitudinal direction Z (the same diameter as the wide-diameter portion 14), in an etching solution and dissolving it. For example, if the glass portion 11 is quartz glass, hydrofluoric acid or buffered hydrofluoric acid (BHF) may be used as the etching solution.

[0028] Adhesive 30 is placed around the narrow-diameter portion 13 and the tapered portion 15. The adhesive 30 has the function of fixing the glass portion 11 (bare portion 12) to the ferrule 20. The volume of the adhesive 30 changes when it hardens. For example, when the adhesive 30 is heated to harden, the adhesive 30 expands due to the heat and then contracts as it cools.

[0029] Here, the tapered portion of the optical fiber is prone to breakage due to stresses such as curing shrinkage of the adhesive used to fix the optical fiber to the ferrule, thermal testing, and vibration testing of the optical fiber, as the diameter changes along the longitudinal direction. In particular, if the surface smoothness of the tapered portion is insufficient, excessive stress can occur in the tapered portion, making it prone to breakage and preventing sufficient tensile strength from being obtained in the optical fiber. In this embodiment, the surface of the tapered portion 15 is formed smoothly. Specifically, the surface roughness (arithmetic mean roughness) Ra of the tapered portion 15 is less than 0.15 μm. Therefore, breakage of the tapered portion 15 due to the above stress can be suppressed, and sufficient tensile strength of the optical fiber 10 can be obtained. It is desirable that the tensile strength of the optical fiber formed by etching be around 3500 MPa. Figure 7 is a graph (experimental results) showing the relationship between the surface roughness Ra of the optical fiber and the tensile strength of the optical fiber. As shown in Figure 7, the smaller the surface roughness Ra of the optical fiber, the greater the tensile strength of the optical fiber 10. From the graph in Figure 7, it was found that when the surface roughness Ra of the optical fiber is reduced to less than 0.15 μm, an optical fiber with a tensile strength of 3500 MPa or more (i.e., having sufficient tensile strength) can be obtained.

[0030] Furthermore, the inventors of this application also confirmed the relationship between other indicators of surface roughness and the tensile strength of the optical fiber. As a result, it was found that, for the surface roughness (maximum height roughness) Rz of the optical fiber, if the maximum height roughness Rz is less than 0.50 μm, an optical fiber with a tensile strength of 3500 MPa or more (i.e., sufficient tensile strength) can be obtained. For the surface roughness (arithmetic mean height) Sa of the optical fiber, it was found that if the arithmetic mean height Sa is less than 0.15 μm, an optical fiber with a tensile strength of 3500 MPa or more (i.e., sufficient tensile strength) can be obtained. For the surface roughness (maximum height Sz) of the optical fiber, it was found that if the maximum height Sz is less than 1.50 μm, an optical fiber with a tensile strength of 3500 MPa or more (i.e., sufficient tensile strength) can be obtained.

[0031] Furthermore, the surface roughness (arithmetic mean roughness) Ra of optical fibers typically produced by spinning or melt-drawing is, for example, about 0.005 to 0.01 μm, and despite being a glass material, it possesses practical strength. The surface roughness (arithmetic mean roughness) Ra of the narrow-diameter portion of an optical fiber created by etching can also be controlled to, for example, about 0.005 to 0.01 μm. In this embodiment, it is preferable that the surface roughness (arithmetic mean roughness) Ra of the narrow-diameter portion 13 of the optical fiber 10 formed by etching is, for example, about 0.005 to 0.01 μm. If the surface roughness Ra of the tapered portion 15 is equivalent to the surface roughness Ra of the narrow-diameter portion 13, the surface will not be discontinuous between the tapered portion 15 and the narrow-diameter portion 13, and the strength of the optical fiber 10 will be higher. Therefore, it is more preferable that the surface roughness Ra of the tapered portion 15 is less than 0.01 μm. In Examples 1 to 3, optical fibers 10 with a surface roughness Ra of the tapered portion 15 less than 0.01 μm were fabricated. The tensile strength of the optical fiber 10 in Example 1 was 4600 MPa, the tensile strength of the optical fiber 10 in Example 2 was 4900 MPa, and the tensile strength of the optical fiber 10 in Example 3 was 4700 MPa, demonstrating sufficient tensile strength. On the other hand, as a comparative example, when an optical fiber with a surface roughness Ra of the tapered portion greater than 0.15 μm was fabricated, the tensile strength of the optical fiber was 1300 MPa, indicating that sufficient tensile strength was not obtained.

[0032] Furthermore, in this embodiment, the diameter of the tapered portion 15 continuously decreases from the first end 15a to the second end 15b. In addition, the outer shape of the tapered portion 15 is symmetrical with respect to the axis O of the optical fiber 10. With these configurations, the fracture of the tapered portion 15 due to the above-mentioned stress can be more effectively suppressed, and sufficient tensile strength of the optical fiber 10 can be obtained.

[0033] Furthermore, microbend loss is known as one of the optical losses in optical fibers. If the surface of the tapered portion is not smooth enough, irregularities are formed on the surface of the tapered portion, making it easy for microbends to occur in the optical fiber. In this embodiment, since the surface of the tapered portion 15 is formed smoothly, irregularities are not formed on the surface of the tapered portion 15, and the occurrence of microbends in the optical fiber 10 can be suppressed. Therefore, the optical loss of the optical fiber 10 can be suppressed.

[0034] Next, an example of a method for manufacturing the optical fiber 10 will be described. In this embodiment, the optical fiber 10 is manufactured using a manufacturing apparatus 60. As shown in Figure 4, the manufacturing apparatus 60 includes a gripping unit 61, a drive unit 62, a container 63, a temperature regulator 64, and a control unit 65.

[0035] The gripping unit 61 grips the optical fiber 10. The drive unit 62 moves the optical fiber 10 gripped by the gripping unit 61 in a sinusoidal manner in the vertical direction. As will be described in detail later, moving the optical fiber 10 in a sinusoidal manner in the vertical direction means that the graph showing the time displacement of the vertical position of any part of the optical fiber 10 is sinusoidal. The container 63 contains the etching solution L. The temperature controller 64 is provided inside the container 63 and adjusts the temperature of the etching solution L contained in the container 63 so that the temperature of the etching solution L is constant (for example, within ±1°C of the target temperature).

[0036] The control unit 65 controls the drive unit 62 and the temperature controller 64. The control unit 65 can adjust the diameter of the narrow-diameter section 13 and the tapered section 15, the length of the tapered section 15 in the longitudinal direction Z, the taper angle θ, etc., by controlling, for example, the amplitude and frequency of the sine wave in the drive unit 62, the driving time of the drive unit 62, etc. The control unit 65 is equipped with a processor such as a CPU (Central Processing Unit) and memory. The processor performs calculations to execute the functions of the control unit 65. The memory stores a rewritable program that describes the functions to be executed by the CPU. The control unit 65 may implement these functions using hardware (including the circuitry) such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or GPU (Graphics Processing Unit). Alternatively, the functions of the control unit 65 may be implemented through the cooperation of software and hardware.

[0037] The manufacturing method for the optical fiber 10 of this embodiment comprises a preparation step and an etching step. In the preparation step, first, an optical fiber 10 having a coating C is prepared. The coating C is partially removed from the optical fiber 10 to expose the glass portion 11. The portion of the glass portion 11 from which the coating C has been removed becomes the bare portion 12.

[0038] Subsequently, in the etching process, the optical fiber 10 is gripped by the gripping unit 61. At this time, the gripping unit 61 grips the optical fiber 10 such that the longitudinal direction Z of the optical fiber 10 coincides with the vertical direction and the bare portion 12 faces downward. The tip of the bare portion 12 is immersed in the etching solution L contained in the container 63, and the optical fiber 10 is moved sinusoidally in the vertical direction by the drive unit 62. That is, the optical fiber 10 is moved up and down continuously multiple times by the drive unit 62. The optical fiber 10 continues to move up and down while the drive unit 62 is being driven. The stopping time of the optical fiber 10 while the drive unit 62 is being driven is less than 1 second.

[0039] The movement of the optical fiber 10 will be explained in detail with reference to Figure 5. Figure 5 is a graph showing the vertical time displacement of the first end 15a of the tapered portion 15 of the optical fiber 10. In Figure 5, the vertical axis represents the vertical position (height) of the first end 15a of the tapered portion 15, and the horizontal axis represents time. Let P1 be the vertical position of the first end 15a when the optical fiber 10 is at its highest point, and let P2 be the vertical position of the first end 15a when the optical fiber 10 is at its lowest point. As shown in Figure 5, the vertical position of the first end 15a of the tapered portion 15 displaces sinusoidally over time between position P1 and position P2. The distance between position P1 and position P2 is the length Z in the longitudinal direction of the tapered portion 15.

[0040] The liquid level La of the etching solution L contained in container 63 is set to position P2. As a result, when the optical fiber 10 is at its highest point, the second end 15b of the tapered portion 15 and the smaller diameter portion 13 located below it are immersed in the etching solution L. When the optical fiber 10 is at its lowest point, the entire tapered portion 15, including the first end 15a, and the smaller diameter portion 13 are immersed in the etching solution L. When the optical fiber 10 is located between the highest and lowest points, a portion of the tapered portion 15 towards the tip and the smaller diameter portion 13 are immersed in the etching solution L. Therefore, the time the tapered portion 15 is immersed in the etching solution L is shortest at the first end 15a, longest at the second end 15b, and gradually increases from the first end 15a to the second end 15b. In this way, by changing the immersion time in the etching solution L for each position in the longitudinal direction Z of the tapered portion 15, the diameter of the tapered portion 15 can be continuously reduced from the first end 15a to the second end 15b.

[0041] As described above, in this embodiment, the optical fiber 10 is immersed in the etching solution L and moved up and down continuously multiple times to form the narrow diameter portion 13 and the tapered portion 15. At this time, the optical fiber 10 is continuously moving up and down, and the stopping time of the optical fiber 10 is less than 1 second. This makes it possible to form a smooth surface for the tapered portion 15. That is, conventionally, the narrow diameter portion and the tapered portion were formed by gradually pulling up the optical fiber immersed in the etching solution to change the immersion time in the etching solution. In this case, no flow of the etching solution is generated in the container, and the reacted etching solution tends to accumulate around the optical fiber. As a result, the etching of the optical fiber does not proceed evenly, and irregularities are formed on the surface of the tapered portion, resulting in insufficient smoothness. In this embodiment, by moving the optical fiber 10 up and down continuously multiple times, a flow of the etching solution is generated in the container. Therefore, the accumulation of reacted etching solution around the optical fiber 10 is suppressed, and the etching solution before reaction can be continuously supplied to the optical fiber 10. As a result, the etching of the optical fiber 10 proceeds evenly, and a smooth surface for the tapered portion 15 can be formed. Furthermore, a tapered portion 15 with good symmetry can be formed around the axis O of the optical fiber 10.

[0042] Furthermore, in conventional methods, when an optical fiber immersed in an etching solution is gradually pulled up, fluctuations in the pulling speed and evaporation of the etching solution prevent the diameter of the tapered section from being continuously reduced, resulting in sections where the diameter of the tapered section remains constant in the longitudinal direction. In this embodiment, since the optical fiber 10 is moved up and down continuously multiple times, fluctuations in the movement speed of the optical fiber 10 and the effects of evaporation of the etching solution are less likely to occur, and the diameter of the tapered section 15 can be continuously reduced.

[0043] As described above, the optical fiber 10 of the present embodiment includes a small-diameter portion 13, a large-diameter portion 14 having a diameter larger than that of the small-diameter portion 13, and a taper portion 15 located between the small-diameter portion 13 and the large-diameter portion 14, the diameter of which gradually decreases from the large-diameter portion 14 side toward the small-diameter portion 13 side. The surface roughness of the taper portion 15, specifically, the arithmetic mean roughness Ra is less than 0.15 μm. Also, the manufacturing method of the optical fiber 10 of the present embodiment has an etching step of etching the optical fiber 10 by moving the optical fiber 10 up and down while immersed in the etching solution L. In the etching step, the optical fiber 10 is continuously moved up and down a plurality of times such that the stop time of the up and down movement of the optical fiber 10 is within 1 second.

[0044] According to such a configuration, the surface of the taper portion 15 is smooth, and sufficient tensile strength of the optical fiber 10 can be obtained.

[0045] Also, the arithmetic mean roughness Ra of the taper portion 15 is less than 0.01 μm. According to this configuration, the tensile strength of the optical fiber 10 can be further improved.

[0046] Also, the surface roughness of the taper portion 15, specifically, the maximum height roughness Rz is less than 0.50 μm. The surface roughness of the taper portion 15, specifically, the arithmetic mean height Sa is less than 0.15 μm. The surface roughness of the taper portion 15, specifically, the maximum height Sz is less than 1.50 μm. According to such a configuration, sufficient tensile strength of the optical fiber 10 can be obtained.

[0047] The length of the taper portion 15 in the longitudinal direction Z is 0.5 to 15 mm.

[0048] When the taper angle θ of the taper portion 15 is considered, 0.1 degree < θ < 5 degrees. According to this configuration, it is possible to suppress the stress such as the curing shrinkage of the adhesive 30 and the thermal test and vibration test of the optical fiber 10 from concentrating on the taper portion 15. Therefore, the tensile strength of the optical fiber 10 can be further improved.

[0049] (Second Embodiment) Next, the second embodiment according to the present invention will be described. The basic configuration is the same as that of the first embodiment. For this reason, the same reference numerals are given to the same configurations and the description thereof is omitted, and only the differences will be described.

[0050] As shown in Figure 6, in this embodiment, the gripping section 61 of the manufacturing apparatus 60 grips a plurality of optical fibers 10. At this time, the distance between the plurality of optical fibers 10 gripped by the gripping section 61 is 1 mm or more. The drive unit 62 simultaneously moves the plurality of optical fibers 10 gripped by the gripping section 61 in a sinusoidal manner in the vertical direction. In the manufacturing method of the optical fibers 10 according to this embodiment, in the etching process, the drive unit 62 drives the plurality of optical fibers 10 simultaneously in a sinusoidal manner in the vertical direction.

[0051] As described above, in the manufacturing method of the optical fiber 10 of this embodiment, in the etching process, multiple optical fibers 10 are moved up and down simultaneously, and the distance between multiple optical fibers 10 is 1 mm or more. This allows etching to be performed on multiple optical fibers 10 simultaneously. Furthermore, even when etching multiple optical fibers 10 simultaneously, a tapered portion 15 with good symmetry can be formed around the axis O of the optical fiber 10, and sufficient tensile strength of the optical fiber 10 can be obtained. That is, when multiple optical fibers are densely arranged in the etching process, when multiple optical fibers are immersed in the etching solution, the etching solution rises due to surface tension, resulting in uneven etching of the optical fibers and an asymmetrical outer shape of the tapered portion around the axis of the optical fiber. In this embodiment, since the distance between multiple optical fibers 10 in the etching process is 1 mm or more, the uneven etching due to surface tension described above can be prevented, and a tapered portion 15 with good symmetry can be formed around the axis O of the optical fiber 10.

[0052] The technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0053] For example, in the above embodiment, it was explained that the optical fiber 10 is moved sinusoidally in the vertical direction during the etching process. However, in the etching process, the optical fiber 10 can be moved up and down continuously multiple times, and the movement of the optical fiber 10 is not limited to sinusoidal motion.

[0054] Furthermore, without departing from the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described embodiments and modifications may be combined as appropriate.

[0055] 10...Optical fiber 13...Narrow diameter section 14...Large diameter section 15...Tapered section θ...Taper angle

Claims

1. An optical fiber comprising: a narrow diameter portion; a wider diameter portion having a larger diameter than the narrow diameter portion; and a tapered portion located between the narrow diameter portion and the wider diameter portion, wherein the diameter gradually decreases from the wider diameter portion side toward the narrow diameter portion side, and the surface roughness of the tapered portion, with the arithmetic mean roughness Ra being less than 0.15 μm.

2. The optical fiber according to claim 1, wherein the arithmetic mean roughness Ra of the tapered portion is less than 0.01 μm.

3. The optical fiber according to claim 1, wherein the surface roughness of the tapered portion, the maximum height roughness Rz, is less than 0.50 μm.

4. The optical fiber according to claim 1, wherein the surface roughness of the tapered portion, the arithmetic mean height Sa, is less than 0.15 μm.

5. The optical fiber according to claim 1, wherein the surface roughness of the tapered portion, with a maximum height Sz, is less than 1.50 μm.

6. The optical fiber according to any one of claims 1 to 5, wherein the length of the tapered portion in the longitudinal direction of the optical fiber is 0.5 to 15 mm.

7. The optical fiber according to any one of claims 1 to 6, wherein when the angle between the tangent to the surface of the tapered portion and the axis of the optical fiber along the longitudinal direction of the optical fiber is defined as the taper angle θ, 0.1 degrees < θ < 5 degrees.

8. A method for manufacturing an optical fiber, comprising an etching step of etching the optical fiber by immersing it in an etching solution and moving it up and down, wherein in the etching step, the optical fiber is moved up and down continuously multiple times such that the stopping time of the up and down movement of the optical fiber is 1 second or less.

9. The method for manufacturing optical fibers according to claim 8, wherein in the etching step, a plurality of optical fibers are moved up and down simultaneously, and the distance between the plurality of optical fibers is 1 mm or more.

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